1. Field of the Invention
The invention relates to a method for detecting a degree of wetting of a glass pane, in particular a windscreen of a motor vehicle, where electromagnetic waves are emitted by a transmitter arranged on the inside relative to the glass pane, which are reflected according to the total reflection principle on the outer, from the transmitter's point of view the opposite surface of the glass pane, and which are received by a receiver arranged on the inside of the pane. Furthermore the invention relates to a sensor unit for detecting a degree of wetting of a glass pane, in particular a windscreen of a motor vehicle, with a transmitter arranged on the inside relative to the glass pane, which emits electromagnetic waves reflected according to the total reflection principle on the outer, from the transmitter's point of view the opposite surface of the pane, and with a receiver arranged on the inside relative to the pane, which receives the reflected electromagnetic waves.
2. Brief Discussion of the Related Art
Sensor units of this kind are known. Sensor means working according to the principle of total reflection are, for example, described in the DE 40 06 174 C1, the DE 197 46 351 A1, the DE 103 39 696 B4 and the DE 35 32 199 A1.
Apart from sensor units working according to the total reflection principle there are sensor units which operate with scattered light. Here electromagnetic waves are directed at as steep an angle as possible at the windscreen and penetrate the windscreen and are scattered on droplets, ice or other particles in front of the windscreen. The electromagnetic waves thus scattered are then received by a receiver arranged on the inside relative to the windscreen. Based on this evaluation conclusions can also be drawn as to the degree of wetting of the windscreen. Such a sensor unit has been described, for example, in the US 2011/0128543 A1.
Furthermore capacitive measuring methods are feasible, with which the degree of wetting of a glass pane may be measured. Such capacitive measuring methods have, for example, been described in the DE 10 2007 035 905 A1 and the EP 1 306 276 B1.
A generic publication is also known from the DE 103 11 800 A1. Further comparatively similar methods and devices are known from the DE 195 30 289 A1 and the DE 10 2004 047 215 A1.